1. Field of Invention
This invention relates to an electrophotographic process suitable for use in electrophotography and, more specifically, to an electrophotographic process of reducing seam marks from an endless seamed organophotoreceptor belt on prints produced by the process.
2. Background of the Art
In electrophotography, an organophotoreceptor in the form of a plate, belt, or drum having an electrically insulating photoconductive element on an electrically conductive substrate is imaged by first uniformly electrostatically charging the surface of the photoconductive element, and then exposing the charged surface to a pattern of light. The light exposure selectively dissipates the charge in the illuminated areas, thereby forming a pattern of charged and uncharged areas. A liquid or solid toner is then deposited in either the charged or uncharged areas to create a toned image on the surface of the photoconductive element. The resulting visible toner image can be fixed to the photoreceptor surface or transferred to a surface of a suitable receiving medium such as sheets of material, including, for example, paper, metal, metal coated substrates, composites and the like. The imaging process can be repeated many times on the reusable photoconductive element.
The photoconductive element usually comprises a charge generating layer, a charge transport layer, and optionally other layers such as a barrier layer, a release layer, an adhesive layer, and a sub-layer. The purpose of the charge generating material is to assist in the generation of charge carriers (i.e., holes or electrons) upon exposure to light. The purpose of the charge transport material is to assist in accepting these charge carriers and transport them through the charge transport layer in order to discharge a surface charge on the photoconductive element.
It is a common practice to have the organophotoreceptor in the form of belt. Although it is ideal to provide a seamless organophotoreceptor belt, where there is no seam in the belt which mechanically or electrostatically interferes with any operation that the belt performs or any operation that may be performed on the belt, the manufacture of seamless organophotoreceptor belts requires rather sophisticated manufacturing processes which are expensive and difficult to control. As a result, seamed organophotoreceptor belts are widely used in electrophotographic applications. Current techniques to manufacture seamed organophotoreceptor belts have largely relied on belts where the two ends of the organophotoreceptor belt material have been lapped or overlapped to form the seam or have butted against one another to form a seam. The seam is then fastened by heat or other means of adhesion such as by the use of an adhesive or welding techniques, such as ultrasonic welding or laser welding. Preferably, seamed organophotoreceptor belts are ultrasonically welded.
In the process of printing, ink is physically attracted to the seam or adsorbed into the seam of the organophotoreceptor belt and subsequently leaves an unattractive seam mark in the prints. The seam mark results from the ink in the seam being offset by the transfer roll during transfer of printed ink to paper. There are two phenomena that make contributions to the seam mark. They are 1) low solid (less than 5% by weight solids in the ink, less than 4.5% by weight, less than 4% by weight, and less than 3.5% by weight solids in the ink, e.g., xcx9c3%) ink which xe2x80x9chidesxe2x80x9d in the roughness of the seam and is squeezed out by the transfer roll to make a very light seam mark on prints and 2) high solid ink (e.g., at least 80%, at least 85%, or equal to or greater than 90% by weight of solids) which is plated directly to the seam as it passes through each developer nip during printing and this contribution causes a very dark seam mark stain on prints.
There has been some work on eliminating the seam mark by coating the seams with materials with low conductivity. However, these attempts have not proven to be commercially acceptable, displaying reduced effectiveness either immediately or after a few hundred prints.
There has also been some work on eliminating the seam mark by continuously cleaning the transfer roll to prevent the offsetting of the seam mark on prints. Such cleaning methods also have been generally ineffective technologically or are not cost effective.
The smoothing of the seam by a belt welder can eliminate the contribution from the low solid ink. However, the plated ink on the seam cannot be eliminated by just smoothing of the seam. In order to eliminate plated ink from reaching the seam, the process condition for plating has to be changed momentarily for each developer station individually as the seam passes through the corresponding developer roll. This momentary change in the process condition can force the ink particles away from the seam. Consequently, the contribution from the high solids ink (plated ink) will be eliminated and no seam mark will show on prints. This adds an additional and potentially complex control step into the imaging process.
This invention eliminates seam mark from a seamed organophotoreceptor belt on prints by changing the electrical voltage of a developer roll momentarily when the seam passes through a developer roll. If there is more than one developer roll in the imaging apparatus, the momentary voltage change in each of the developer rolls takes place in turn when the seam passes through each of them sequentially.
In a first aspect, the invention features an electrophotographic imaging process that includes:
(a) providing an organophotoreceptor belt having 1) a photoconductive element on an electrically conductive substrate and 2) a seam (b) providing an imaging apparatus comprising a developer roll;
(c) mounting the organophotoreceptor belt on the imaging apparatus (d) applying a first voltage to the photoconductive element;
(e) after applying the first voltage, applying a second voltage to the developer roll when the seam is at a distance less than 10% of the circumference of the organophotoreceptor belt from the developer roll, and subsequentlly applying a third voltage to the developer roll;
(f) applying a fourth voltage to the electrically conductive substrate; (g) moving the organophotoreceptor belt;
(h) imagewise exposing the surface of the organophotoreceptor belt to radiation to reduce voltage in selected areas and thereby form a pattern of high voltage and low voltage areas on the surface;
(i) contacting the surface with a liquid ink comprising colorant particles in an organic liquid to create an image; and
(j) transferring the toned image to a receiving medium; wherein
A) the second voltage is equal to or less than the fourth voltage when the first voltage and third voltage are positive or
B) the second voltage is equal or greater than the fourth voltage when the first voltage and third voltage are negative.
In a second aspect, the invention features an electrophotographic imaging process that includes:
(a) providing an organophotoreceptor belt having a photoconductive element on an electrically conductive substrate and a seam;
(b) providing an imaging apparatus comprising a developer roll and a squeegee roller;
(c) mounting the organophotoreceptor belt on the imaging apparatus;
(d) applying a first voltage to the photoconductive element;
(e) applying a second voltage to the developer roll when the seam is at a distance less than 10% of the circumference of the organophotoreceptor belt from the developer roll, subsequently applying a third voltage;
(f) applying a fourth voltage to the electrically conductive substrate;
(g) applying a fifth voltage to the squeegee roller;
(h) moving the organophotoreceptor belt;
(i) imagewise exposing the surface of the organophotoreceptor belt to radiation to reduce voltage in selected areas and thereby form a pattern of high voltage and low voltage areas on the surface;
(j) contacting the surface with a liquid ink comprising colorant particles in an organic liquid to create an image; and
(k) transferring the toned image to a receiving medium;
wherein A) the second voltage is equal or less than the fourth voltage when the first and third voltage are positive or B) the second voltage is equal or greater than the fourth voltage when the first and third voltage are negative. In the description of the process, steps are separated by alphanumeric headings for convenience, not necessarily for identifying a sequence. As is apparent to one skilled in the art, the sequence of steps may be reversed, such as the order in which the individual dispersions are prepared, and the like. Unless a sequence of steps is identified as being in sequence (as with identifying charging steps as first, second, third, and fourth charging steps), no sequence is required, except for those necessarily in sequence, as where a dispersion is coated, and the solids must have been dispersed before coating.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof and from the claims.